This invention relates generally to pulse detonation engines and more particularly to pulse detonation engines utilizing magnetohydrodynamic flow control.
Most internal combustion engines currently used for propulsion rely on deflagration combustion whereby the combustion effects occur at relatively slow rates (i.e., less than the speed of sound within the combustible mixture) and at constant pressure. Detonation combustion, however, occurs at rates well in excess of the speed of sound and simultaneously provides a significant pressure rise. Because of the advantageous thermodynamic cycle, there is a high degree of interest in developing propulsive devices that rely on detonation combustion rather than deflagration combustion.
One such device is a pulse detonation engine that uses an intermittent combustion process to create a temperature and pressure rise by detonating a flammable mixture. The conditions for detonation are governed by the environment of the mixture (pressure, temperature, equivalence ratio, etc.) such that when enough energy is released to start ignition, the chemical kinetics occur at supersonic speeds. A pulse detonation engine is typically a tube of a specified length that is open at the aft end and includes some sort of valve device at the front end to keep the detonation process from traveling forward. In operation, a charge of air and fuel is fed into the tube through the valve, and the valve is then closed. Detonation of the fuel-air mixture is initiated by an igniter located in the tube, and the resulting detonation shock waves travel down the tube, raising both the temperature and the pressure of the products. The combustion products are expelled out of the open aft end, creating a pulse of forward thrust. When the shock waves have reflected within the tube to the appropriate conditions, a new charge is fed into the tube through the valve and the cycle repeats. It is generally desirable to generate pulses at a high frequency to produce smooth, nearly steady state propulsion.
Upon ignition, the resulting pressure waves and detonation flame front will tend to travel in both longitudinal directions. In current pulse detonation devices, however, ignition is initiated at the forward end of the tube so that the waves will generally travel downstream toward the open exhaust end. The valve is provided at the forward end of the tube to prevent pressure waves from escaping out the front of the device and, more importantly, to prohibit the detonation flame front from traveling into the fuel-air inlet system. The pulse detonation cycle requires that the valve operate at extremely high temperatures and pressures and must also operate at exceedingly high frequencies to produce smooth propulsion. These conditions significantly reduce the high cycle fatigue (HCF) reliability of conventional valve systems, such as poppet or flapper-type valves.
Accordingly, it would be desirable to have a high frequency valving or flow control system for pulse detonation engines that is lightweight, reliable, easily controlled and offers minimal performance loss.
The above-mentioned need is met by the present invention, which provides a pulse detonation engine that includes a tube having an open forward end and an open aft end and a fuel-air inlet formed in the tube at the forward end. An igniter is disposed in the tube at a location intermediate the forward end and the aft end. A magnetohydrodynamic flow control system is located between the igniter and the fuel-air inlet for controlling detonation in the tube forward of the igniter. The magnetohydrodynamic flow control system creates a magnetic field forward of the igniter to dissipate the forward traveling detonation flame front.
The present invention and its advantages over the prior art will become apparent upon reading the following detailed description and the appended claims with reference to the accompanying drawings.